1. Field of the Invention
The present invention relates to an apparatus for chemical vapor deposition (CVD) that is one of effective means for forming a film on a semiconductor integrated circuit, a fine mechanical structure, or a tool which requires surface treatments, and more particularly, to an apparatus for chemical vapor deposition (CVD) with a showerhead and method thereof, that can prevent a undesired particle deposition on the showerhead which supplies reactive gases uniformly over a substrate to grow a uniform film on the substrate in thickness and composition. Here, the present invention is associated with U.S. Patent Laid-Open Publication No. 2003-6077388 (“Method And Apparatus For Chemical Vapor Deposition Capable Of Preventing Contamination And Enhancing Film Growth Rate” filed on Oct. 9, 2002), the entire contents of which are hereby incorporated by reference.
2. Background Art
In an apparatus for chemical vapor deposition (CVD), a reactive gas is introduced into a vacuum reaction chamber, passes through a showerhead, then reaches a susceptor or a substrate holder on which a substrate is located.
Therefore, the reactive gas causes chemical reaction on the substrate to form a desired film. As means to provide energy necessary to induce chemical reactions on the substrate, a method of simply heating the substrate or atomically exciting the reactive gas, such as making plasma, is widely used. After the reaction is finished, byproduct gases are removed from the reaction chamber by an exhaust system including a vacuum pump, passes through a purifying system, then discharged into the atmosphere. However, since it is very important to prevent undesired particle deposition on a wall of the reaction chamber or the showerhead during a deposition process, it is preferable that the reactive gases do not react each other in a gaseous state. Unfortunately, if reactive gases whose decomposition temperature are substantially lower than 200° C. like metal-organic compounds are mixed in the reaction chamber, the mixture may cause homogeneous reactions in the gas phase so as to generate contaminant particles, or cause heterogeneous reactions on a solid-state surface, such as the showerhead surface or the reaction chamber wall so as to deposit undesired particles. Particularly, it may happen that the reactive gas is sensitive to a specific material, for example, zirconium tert-butoxide (Zr(OC4H9)4) is extremely sensitive to moisture so as to form zirconium hydroxide (Zr(OH)x) which is a powder. The moisture could have been physically adsorbed on the inner side of the reaction chamber but it may be also generated over the substrates as a byproduct gas.
Such moisture reacts with Zr(OC4H9)4 on the inner wall of the reaction chamber or the surface of the showerhead, depositing a zirconium hydroxides of white powder type on the surface thereof. Then, the deposited particles are flaked off into fine particles due to a repeated thermal expansion and contraction and/or a lattice parameter mismatch with the inner wall of the reaction chamber. As a result of this, the film formed on the substrate may be contaminated and the productivity may be lowered due to a shortened process management cycle time for removing the deposited particles.
When a highly integrated semiconductor is manufactured, contaminant particles may cause a pattern defect such as short or disconnection between lines, and a size of the contaminant particle influencing on yield is in proportion to the line width. Therefore, as the line size becomes smaller, that is, as the density of the integration is increased, the size of particle influencing on yield becomes also smaller, whereby the number of contaminant particles to be controlled in the reaction chamber is more seriously limited.
FIG. 1 is a brief sectional view of a reaction chamber of a conventional plate type plasma CVD apparatus using a simple showerhead having a large number of holes as described in U.S. Pat. No. 6,631,692. When the reaction chamber is maintained in a vacuum state by a vacuum pump (not shown), material gases, that is, reactive gases flowing from a material gas supply tank is controlled by a mass flow controller 8 at a preferable flow rate, and the material gas delivered into a showerhead 20 is supplied on a substrate through fine holes formed on the bottom surface of the showerhead after being mixed sufficiently. After a flow is stabilized, a radio frequency (RF) electric field is generated between the showerhead 20 connected to an RF power source 4 and a susceptor grounded to an earth 13, and then, the material gas is ionized and the plasma state occurs. Atoms of the ionized material gas shows a chemical reaction on a semiconductor substrate 9 located on the susceptor 30, which keeps temperature of the substrate higher than that of surroundings using a substrate heater 14 embedded in the reaction chamber, whereby a desirable film is formed on the substrate 9. As a material gas, the silicon source gases such as SiH4, DM-DMOS[(CH3)2Si(OCH3)2], and TEOS, fluorine source gases such as C2F6, oxidizing gases such as oxygen, and inert gases such as Ar and He can be used.
There may be no serious problem when one of the above raw materials is used solely, but in case when a specific material, for example, metal-organic compound of a low decomposition temperature, is used as the material gas, the material gas may cause chemical reaction inside the showerhead or generate contaminant particles by decomposing by itself, thereby contaminating the inside of the reaction chamber and the surface of the substrate.
FIG. 2 shows a schematic sectional view of a showerhead of a prior art, U.S. Pat. No. 6,626,998, that has a function to uniformly spray reactive gas, which is introduced into a reaction chamber, over a substrate through a plurality of outlets without gas mixing. When each reactive gas is supplied to first ring type individual channels 23 through a plurality of gas supply passages 17, the gases are diffused in the first individual channels 23, and then, transmitted to second ring type individual channels 27 through a plurality of transition passages 25 formed on the bottom of each channel. After diffusion of the reactive gases in the second channels 27, the gases are supplied over a substrate through a plurality of second gas transition passages 31 which are formed on the bottom of the second channels. The reactive gases cause chemical reaction on the substrate (not shown) placed on a susceptor keeping temperature of the substrate higher than that of surroundings so as to form a desired film on the substrate.
However, a reactive gas such as metal-organic compound gas which has a decomposition temperature of about 200° C. or below may cause heterogeneous surface reactions including a thermal decomposition on the bottom surface of the showerhead, and particularly, if the reactive gas is sensitive to a specific material like moisture, the reactive gas may form unwanted deposits on the bottom of the showerhead by combining with the moisture produced as a byproduct.
With regard to the contamination path described above, FIG. 3 shows that the reactive gas or byproduct gas may reversely diffuse toward the showerhead in case that there is not provided suitable suppressing means. In FIG. 3, a thin arrow indicates an average drift flow of the reactive gases, and a thick arrow indicates a reverse diffusion direction of the reactive gases or byproducts toward the showerhead. The byproducts generated over the substrate may be reversely diffused toward a zone 8 existing between the showerhead and the substrate, and the gases in the zone 8 may be also reversely diffused toward the showerhead. Therefore, even if the conventional showerhead device shown in FIG. 2 may prevent each reactive gas from being mixed inside the showerhead and generating particles, in case that there is not provided suitable suppressing means, undesired particles may be deposited on the bottom of the showerhead by thermal decompositions or other chemical reactions. And this problem is especially serious if the substrate temperature becomes higher.
A necessity to form various kinds of films using various kinds of reactive gases by CVD process has been increased. However, if the conventional showerhead device is used further, undesired particles may deposit on the bottom of the showerhead due to the unexpected properties of the reactive gases used, which may limit the wide application of the CVD process.